The disclosure relates to devices which automatically detect their location with respect to a defined area and perform a function when a boundary of the defined area is reached or crossed. For example, such devices may be mobile working devices such as automatic or semi-automatic ground treatment machines, for example lawnmowers and the like.
Automatic or semi-automatic mobile working devices, for example ground treatment machines, for example lawnmowers, are generally intended to automatically move inside a defined working area without leaving the latter. An outer boundary of the working area may be determined, for example, by an electrical boundary conductor.
An electrical current flows through the boundary conductor which marks the outer boundary of the working area. The resultant electrical or magnetic field may be detected by a suitable sensor in the mobile working device, with the result that the working device can perform a function upon approaching the boundary of the working area. In the case of automatic mobile working devices, provision may be made, for example, for the mobile working device to turn or reverse in order to thus avoid leaving the working area.
In a simple embodiment, an electrical alternating current flows through the boundary conductor. The mobile working device is provided with detection coils in which an AC voltage is induced by the alternating magnetic field generated around the boundary conductor. Upon approaching the current-carrying boundary conductor, the magnetic field strength of the alternating field increases, as a result of which the amplitude of the induced AC voltage increases. Upon reaching a defined threshold for the amplitude of the induced AC voltage, the mobile working device is instructed to move away from the boundary of the working area. If the boundary conductor is crossed, the direction of the alternating magnetic field is reversed and the phase angle of the induced AC voltage thus changes, with the result that the mobile working device can use the phase change to discern whether it is inside or outside the working area.
The documents U.S. Pat. No. 3,550,714, U.S. Pat. No. 3,570,227, U.S. Pat. No. 549,674, U.S. Pat. No. 3,407,895, DE 16 13 991 and DE 19 02 037 disclose simple operating area boundaries for mobile working devices, which are based on measuring the signal strength of a signal emitted by a boundary conductor. However, a disadvantage of these systems is that it is not possible to detect on what side of the current-carrying boundary conductor the corresponding detection coil is located, that is to say whether the working device is inside or outside the defined working area. In particular, with this method, it is not possible to determine whether the working device is inside or outside the working area when the mobile working device is switched on.
In the case of systems which have been developed further, as known, for example, from the documents WO 90/00274, EP 1 025 472, EP 1 047 983, DE 2 228 659, U.S. Pat. No. 3,299,351 and U.S. Pat. No. 5,438,266, provision is made for the boundary conductor to have superimposed alternating currents at two or more than two frequencies. If the frequencies of the alternating currents are multiples of one another and their temporal relationship with respect to one another is known, the sum signal can be used to determine on what side of the boundary conductor the mobile working device is located.
The document EP 1 470 460 describes a system which is able, to a limited extent, to detect whether the detection coils in the mobile working device are inside or outside a current-carrying boundary conductor. For this purpose, the amplitudes of the currently detected signals are compared with the previous amplitudes. A microprocessor carries out a numerical analysis in order to determine the number of measurements which is needed to reach a threshold value and which is a measure of the distance to the boundary conductor. The numerical analysis makes it possible to detect a phase change when the boundary conductor is crossed. A further possible way of detecting when the boundary conductor is crossed may involve comparing the signals from two detection coils which are fastened to the mobile working device at different positions. This makes it possible to detect a phase shift as a result of the boundary conductor being crossed.
The documents EP 1 512 053 and EP 1 906 205 each describe a system in which periodic current pulse trains flow through the boundary conductor. The magnetic field generated by the current pulse train is detected by suitable sensors and the resultant voltage signals are evaluated over time.
The disadvantage of the systems described above is that it is necessary to impress alternating currents at two or more than frequencies on the boundary conductor and to carry out a temporal evaluation of the signals which is triggered by a current pulse.
The document EP 1 612 631 describes a system which can carry out an evaluation without a current trigger signal. However, with this system, it is necessary to switch on the mobile working device while it is inside the working area. After the mobile working device has been switched on, a clock in the working device is synchronized with the signal from the boundary conductor. As a result, the working device can detect phase changes when the boundary conductor is crossed.
The object of the present disclosure is to provide a device and a method for operating a device, the device being able to detect whether it is inside or outside a defined area, without previously learning what area it is located in, for example as early as immediately after being switched on.